1/*- 2 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org> 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23 * SUCH DAMAGE. 24 * 25 * $FreeBSD: stable/11/sys/sys/refcount.h 367457 2020-11-07 18:10:59Z dim $ 26 */ 27 28#ifndef __SYS_REFCOUNT_H__ 29#define __SYS_REFCOUNT_H__ 30 31#include <sys/limits.h> 32#include <machine/atomic.h> 33 34#ifdef _KERNEL 35#include <sys/systm.h> 36#else 37#define KASSERT(exp, msg) /* */ 38#endif 39 40static __inline void 41refcount_init(volatile u_int *count, u_int value) 42{ 43 44 *count = value; 45} 46 47static __inline void 48refcount_acquire(volatile u_int *count) 49{ 50 51 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count)); 52 atomic_add_int(count, 1); 53} 54 55static __inline int 56refcount_release(volatile u_int *count) 57{ 58 u_int old; 59 60 atomic_thread_fence_rel(); 61 old = atomic_fetchadd_int(count, -1); 62 KASSERT(old > 0, ("refcount %p is zero", count)); 63 if (old > 1) 64 return (0); 65 66 /* 67 * Last reference. Signal the user to call the destructor. 68 * 69 * Ensure that the destructor sees all updates. The fence_rel 70 * at the start of the function synchronized with this fence. 71 */ 72 atomic_thread_fence_acq(); 73 return (1); 74} 75 76/* 77 * This functions returns non-zero if the refcount was 78 * incremented. Else zero is returned. 79 * 80 * A temporary hack until refcount_* APIs are sorted out. 81 */ 82static __inline __result_use_check int 83refcount_acquire_if_not_zero(volatile u_int *count) 84{ 85 u_int old; 86 87 old = *count; 88 for (;;) { 89 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count)); 90 if (old == 0) 91 return (0); 92 if (atomic_fcmpset_int(count, &old, old + 1)) 93 return (1); 94 } 95} 96 97static __inline __result_use_check int 98refcount_release_if_not_last(volatile u_int *count) 99{ 100 u_int old; 101 102 old = *count; 103 for (;;) { 104 KASSERT(old > 0, ("refcount %p is zero", count)); 105 if (old == 1) 106 return (0); 107 if (atomic_fcmpset_int(count, &old, old - 1)) 108 return (1); 109 } 110} 111 112#endif /* ! __SYS_REFCOUNT_H__ */ 113